The present invention relates to a semiconductor device for suppressing a resistance value of a resistor whose resistance value varies in response to a substrate temperature.
In semiconductor devices, elements of a transistor, a resistance, a capacitor, etc. are formed over a semiconductor substrate. Then, each element has a temperature characteristic which varies depending on the substrate temperature. In addition, a circuit characteristic may vary according to the temperature characteristics of the elements. For example, in an oscillating circuit that determines an oscillating frequency of its output signal using a time constant determined by a resistance value of a resistance and a capacitance value of a capacitor, the oscillating frequency varies according to the temperature characteristic of the resistance. In the oscillating circuit like this, in order to suppress a variation of the oscillating frequency, it is necessary to perform a measure to suppress the variation of the resistance value caused by the temperature characteristic, etc.
Then, a technology of suppressing the variation of the oscillating frequency due to the temperature characteristic of the resistance is disclosed by Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2006-510309. For a reference, FIG. 21 of Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2006-510309 is shown in FIG. 25 and shows a block diagram of an oscillator 200. The oscillator 200 is configured so that two voltage levels used to control the oscillating frequency may be varied, which minimizes the variation of the oscillating frequency by the temperature. A first resistor R1 is used in order to suppress one of voltage levels. A second resistor R2 is used in order to suppress the other voltage level. Here, the first resistor R1 and the second resistor R2 have different temperature coefficients, respectively. Moreover, in addition, the first resistor R1 controls a current used for charging and discharging a capacitor C that generates an oscillation. In an oscillator 200, a control voltage and a current vary so that a time to charge and discharge the capacitor between control voltages may be kept almost constant to the temperature by a suitable selection of a resistance value.
More specifically, in the oscillator 200, the oscillating frequency is dependent on a difference between a first resistance value of the first resistor R1 and a second resistance value of the second resistor R2. Then, the first resistance value is larger than the second resistance value, a resistance value of the first resistor R1 exhibits a first rate of variation to the temperature, and a resistance value of the second resistor R2 exhibits a second rate of variation to the temperature. Furthermore, the second rate of variation is set up so as to be larger than the first rate of variation. By this, in the oscillator 20, a temperature variation of the first resistance value is cancelled out by a temperature variation of the second resistance value, and therefore the variation of the oscillating frequency by the temperature is decreased.